Choose thick walled styrofoam container. Be sure it passes inspection by various farm helpers.
Insert bucket with food to be soaked inside container.
Add water. For alfalfa cubes, I add boiling water to hasten the softening process. For other feed, I add warm or cool water depending on the season. Fill water to the top of the cubes. Alfalfa and hay cubes take some trial and error to find the correct consistency because many horses do not like it to be gruel-like. I have found for one quart of hay cubes, a full hot pot (56 oz) of boiling water achieves the correct result.
Cover and let cubes soak. I keep the coolers on raised containers to help keep them warmer longer in cold weather.
Horses eating soaked foods will spill the wet food everywhere. I feed them inside a water trough so the spilled food is contained for easier cleanup. I have drilled small holes in the bottom of the trough to allow for draining of excess water.